JPH04366584A - Resistance regulating type heater and heater unit - Google Patents

Abstract

PURPOSE:To prevent a short-circuit even under a hard operating condition of automobile and certainly hold the insulating property of a slit. CONSTITUTION:A honeycomb heater 24 has electrodes 21 on a honeycomb structure and a slit 22 between the electrodes. The outside surface 20 of the honeycomb structure and the slit 22 is enameled. A heater unit is manufactured by setting the honeycomb heater 24 in a can body 30, and the surface 32 of a ring 31 possible to make contact with the heater 24 is also enameled.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance-adjustable heater and a heater unit that can be suitably used for purifying automobile exhaust gas.

0002

[Prior Art] Recently, catalysts and catalyst carriers have been developed for purifying nitrogen oxides (NOX), carbon monoxide (CO), and hydrocarbons (HC) in exhaust gas emitted from internal combustion engines such as automobiles. In addition to the conventionally known porous ceramic honeycomb structures, metal honeycomb structures have started to attract attention. On the other hand, as exhaust gas regulations become stricter, there is a strong need for the development of heaters that reduce emissions during cold starts.

[0003] As such a honeycomb structure, the technique described in, for example, Japanese Utility Model Application Publication No. 63-67609 is known. This Japanese Utility Model Publication No. 63-67609 discloses a catalytic converter in which an electrically conductive metal monolith catalyst having a metal carrier coated with alumina is disposed close to the upstream side of a ceramic main monolith catalyst.

0004

However, in the catalytic converter described in Japanese Utility Model Application Publication No. 63-67609, the metal monolith catalyst as a preheater disposed close to the upstream side of the main monolith catalyst is simply a foil. This type of metal honeycomb structure generates heat by passing electricity from the inner periphery to the outer periphery, and the resistance is not adjusted (in other words, the desired resistance is adjusted only by specifying the material, dimensions, and rib thickness). However, there was a problem that the temperature increase characteristics were insufficient.

[0005] Therefore, the applicant of the present invention previously proposed a heater in which a honeycomb structure is provided with at least two electrodes for energizing, and a resistance adjustment mechanism is provided between the electrodes (Japanese Patent Application No. 96866/1999). ). In this heater, the outer periphery of the slits is filled with a zirconia-based heat-resistant inorganic adhesive to insulate the slits. According to this heater, the desired heat generation property can be controlled, and it is useful for reducing emissions of automobile exhaust gas at the time of cold start. The present applicant has also proposed a heater in which an insulating member (spacer) made of ceramic such as alumina is set in a slit provided on the outer periphery of a honeycomb structure, and an insulating part is formed.
A method of holding a honeycomb heater by covering the outer periphery of the honeycomb heater with a metallic band with an insulating material such as a ceramic mat or cloth interposed therebetween was proposed (Japanese Patent Application No. 15880/1999). Furthermore, the patent application Hei 3-15
In No. 880, the band or ring itself is made of Al2, for example.
A method of forming an insulating protective film on the band and ring surfaces by thermally spraying O3 or ZrO2 to form a ceramic coating is also disclosed. All of the above-mentioned methods are methods for insulating and protecting the resistance adjustment mechanism of the heater;
In this case, there is a risk of destruction, which poses a practical problem.

[0006]

[Means for Solving the Problems] The present invention solves the above problems and provides a resistance-adjustable heater and a heater unit that can prevent short circuits and fully exhibit its resistance-adjusting function even under severe operating conditions. The purpose is to provide That is, according to the present invention, there is provided a resistance adjustment type heater in which a honeycomb structure having a large number of through holes is provided with at least two electrodes for supplying electricity, and a resistance adjustment mechanism is provided between the electrodes. A resistance adjustment type heater characterized in that at least a portion forming a resistance adjustment mechanism is coated with an insulating ceramic coating, and a honeycomb structure having a large number of through holes is provided with at least two electrodes for supplying electricity. Also, a resistance-adjustable heater comprising a slit serving as a resistance-adjusting mechanism between the electrodes, the resistance-adjustable heater comprising a metallic spacer coated with an insulating ceramic inserted into the outer periphery of the slit. A heater is provided.

Further, according to the present invention, a resistance adjustment type heater is provided in which a honeycomb structure having a large number of through holes is provided with at least two electrodes for supplying electricity, and a resistance adjustment mechanism is provided between the electrodes. A heater unit held in a can body made of aluminum, wherein at least a portion forming the resistance adjustment mechanism or at least a portion forming the resistance adjustment mechanism and the can body are coated with an insulating ceramic coating. and a resistance-adjustable heater comprising at least two electrodes for supplying electricity to a honeycomb structure having a large number of through-holes, and a slit serving as a resistance-adjusting mechanism between the electrodes. A heater unit held in a metallic can body, in which a metallic spacer coated with an insulating ceramic is inserted into the outer periphery of the slit, and the can body is coated with an insulating ceramic coating. A heating unit is provided, which is characterized by: In the resistance-adjustable heater and heater unit of the present invention, it is preferable that an insulating ceramic coating is further applied to the outer periphery of the resistance-adjustable heater, and the ceramic coating may be applied by enameling. is preferred. Furthermore, it is preferable that the resistance adjustment mechanism is a slit.

[0008]

[Function] In order to prevent a short circuit even under severe operating conditions in a heater having a resistance adjustment mechanism such as a slit, and to fully exhibit its resistance adjustment function, the present invention provides at least a portion forming the resistance adjustment mechanism. This is a resistance adjustment type heater which is coated with an insulating ceramic coating and/or has a metal spacer coated with an insulating ceramic inserted into the outer periphery of a slit serving as a resistance adjustment mechanism. In the case of a heater unit in which these resistance-adjustable heaters are held in a metal can, the can is further coated with an insulating ceramic coating. Since the resistance-adjustable heater and heater unit of the present invention have the above-described configuration, the insulation of the resistance-adjustable mechanism such as the slit can be reliably maintained even under severe driving conditions of an automobile.

[0009] Next, in the present invention, a ceramic coating having an insulating property for fully expressing the resistance adjustment function of the resistance adjustment mechanism such as a slit will be explained. In the present invention, an insulating ceramic coating is applied to the portion forming the resistance adjustment mechanism. If the resistance adjustment mechanism is a slit, there is a risk that the cells of the honeycomb structure will deform during operation and the ribs (partition walls) separating the slits may come into contact with each other, so it is necessary to apply ceramic coating to the slit portions. In this case, as shown in FIG. 2, the coating 12 may be applied to the entire slit portion 10, but for simple use, it is sufficient to coat about 10 mm from the outer peripheral portion 11 for insulation. Furthermore, by applying the ceramic coating 12 to seal the entire slit portion 10, gas can be prevented from blowing through there.
preferable.

Further, in the present invention, it is preferable that a ceramic coating is further applied to the outer peripheral portion of the honeycomb structure, for example, the upper surface, lower surface, or outer surface. That is, from the viewpoint of preventing short circuits, it is preferable to apply a ceramic coating to areas or portions where the heater may come into contact with the can body or the holding member that holds the heater in the can body. Further, in the present invention, as shown in FIG. 3, from the viewpoint of ensuring insulation and preventing deformation of the heater, it is preferable to insert a spacer 13 into the slit portion 10 serving as the resistance adjustment mechanism. As a material for the spacer, a spacer made of ceramic such as alumina is usually considered, but ceramic is hard and brittle and has the disadvantage of being easily damaged. On the other hand, a spacer made of a metallic member coated with a ceramic is preferable because it exhibits the properties of metal and is free from damage. Further, in this case, it is desirable that the metallic member exhibits the same degree of thermal expansion as the material of the heater body.

[0011] Here, the structure of the spacer is not particularly limited, but as shown in Figs. 4 to 6, a structure in which it is inserted about 10 mm from the outer periphery of the heater (Fig. 4), a structure in which it is inserted in the entire slit (Fig. 5), Various structures are possible, such as a structure that integrally holds the outer surface of the heater (FIG. 6). Among the above, the spacer shown in FIG. 4 is preferable because of its simplicity, the spacer shown in FIG. 5 is preferable from the viewpoint of preventing gas from blowing through the slit portion, and the spacer shown in FIG. 6 is preferable from the viewpoint of preventing deformation of the honeycomb structure due to vibration.

[0012] In the present invention, it is preferable to apply a ceramic coating to the slit portion and further insert a spacer into the slit portion, but even if either one of them is insulated, the function can be fully expressed. Examples of the ceramic coating in the present invention include thermal spraying, chemical vapor deposition (CVD), and physical vapor deposition (PVD).
), enameling, dipping, etc., but enameling is preferred because it is simple and has excellent heat resistance and thermal shock resistance.

[0013] Enameling is carried out, for example, as follows. A refractory material such as alumina, chromia, fused silica, clay, etc. and, if necessary, a deflocculant such as acid or alkali are added to the desired heat-resistant frit to obtain a slip-like slip. On the other hand, the surface of a base material made of metal is leveled by sandblasting, etc., and then washed with acid or synthetic detergent, etc., and then glazed with the above-mentioned slurry slip by spraying, dipping, brushing, etc. . Next, after glazing, it goes through a drying process and is heated in a firing furnace for 60 minutes in normal atmosphere.
By firing at a temperature of 0 to 1150°C, enameling is performed on the metallic base material. Typical glaze types include, for example, N. B. S. (U.S. Bureau
of standard) A-19, A-20, A-55
m, A-19H, A-417, A-520, M37~M
41, M13, M43, etc. M13 etc. are fired in an H2 atmosphere at about 1350°C after glazing.

[0014] When selecting a material for the heat-resistant frit, it is preferable to select the material so that its thermal expansion relatively matches that of the base material (for example, in the range of 50% to 100% of the thermal expansion of the base material); The heat resistance of the glazed portion is 400°C or higher, preferably 600°C or higher. The amount of refractory material added to the frit is preferably 5-50%. The amount of refractory material is 5
If it is less than 50%, the heat resistance will be poor, and if it exceeds 50%, the glazing property will be poor. The thickness of the ceramic coating obtained as described above is preferably in the range of 5 to 500 μm. Film thickness is 5μ
If the film thickness is less than 5 m, the desired insulation properties and durability cannot be obtained, and the film thickness is less than 5 m.
If it exceeds 00 μm, chipping and the like will begin to occur, causing problems in film adhesion. Next, in the heater unit of the present invention, the ceramic coating is also applied to the can body. That is,
As mentioned above, a resistance-adjustable heater (honeycomb heater) with various ceramic coatings is held in the can body and used as a heater unit, but the honeycomb heater may come into contact with the can body. It is further preferred that the body part or member is subjected to a ceramic coating treatment. That is, in the present invention, the outer periphery of the honeycomb heater is usually held in a can body by interposing an insulating material such as a ceramic mat or cloth, and using a metal band or ring. Therefore, it is preferable to perform a ceramic coating treatment on these metal members such as bands and rings, and on the inside of the can body itself. Such a heater unit can be arranged upstream or downstream of the main monolithic catalyst to form a catalytic converter, or it can have the catalyst supported on a honeycomb heater and act as a catalytic converter itself. can.

[0015] The constituent material of the honeycomb structure, which is the base of the present invention, is not limited as long as it is made of a material that generates heat when energized, and may be metal or ceramic, but metal has high mechanical strength. Therefore, it is preferable. In the case of metals, for example, stainless steel, Fe-Cr-Al, Fe-C
Examples include those made of materials having compositions such as r, Fe-Al, Fe-Ni, W-Co, and Ni-Cr. Among the above, Fe-Cr-Al, Fe-Cr, and Fe-Al are preferable because they have excellent heat resistance, oxidation resistance, and corrosion resistance, and are inexpensive. The honeycomb structure may be porous or non-porous, but when supporting a catalyst, a porous honeycomb structure has strong adhesion to the catalyst layer and the catalyst is absorbed due to the difference in thermal expansion. This is preferable because peeling hardly occurs.

Next, an example of a method for manufacturing a metallic honeycomb structure among the honeycomb structures of the present invention will be explained. First, to obtain the desired composition, for example, Fe powder, Al powder, C
A metal powder raw material is prepared using R powder or an alloy powder thereof. Next, the metal powder raw material prepared in this way is mixed with an organic binder such as methyl cellulose or polyvinyl alcohol, and water, and then this mixture is extruded into a desired honeycomb shape.

Next, the extruded honeycomb molded body is
Calcinate at 1000-1450°C in a non-oxidizing atmosphere. Here, it is preferable to perform the firing in a non-oxidizing atmosphere containing hydrogen because the organic binder is decomposed and removed using Fe or the like as a catalyst, and a good sintered body (honeycomb structure) can be obtained.

[0018] If the firing temperature is less than 1000°C, the molded body will not be sintered, and if the firing temperature exceeds 1450°C, the obtained sintered body will be deformed, which is not preferable. Note that preferably, the surfaces of the partition walls and pores of the obtained honeycomb structure are coated with a heat-resistant metal oxide.

Next, regarding the obtained honeycomb structure,
A resistance adjustment mechanism is provided between the electrodes in various ways, which will be described later. The resistance adjustment mechanism provided in the honeycomb structure is as follows:
For example, ■ Providing slits in various directions, positions, and lengths; ■ Changing the length of the partition walls in the through-axis direction; ■ Changing the thickness of the partition walls (wall thickness) of the honeycomb structure; or Preferable examples include changing the cell density of the honeycomb structure, and (2) providing slits in the partition walls of the honeycomb structure. Among these, the formation of slits (3) is particularly preferred as a method for easily adjusting the heat generating portion.

[0020] The metallic honeycomb structure obtained as described above is usually provided with electrodes on the partition wall or inside the outer circumference by means of brazing, welding, etc.
A honeycomb type heater is produced. Note that the term "electrode" as used herein is a general term for terminals for applying voltage to the heater, and includes terminals such as those in which the outer circumference of the heater and the can body are directly connected, and terminals such as ground terminals.

[0021] When this metallic honeycomb structure is used as a heater, its overall resistance value is 0.001Ω~
It is preferable to form it so that it may be in the range of 0.5Ω. Further, by further supporting a catalyst on the surface of the above-described metallic honeycomb structure, it is possible to expect a temperature increase due to the exhaust gas purification reaction (oxidation reaction heat, etc.), which is preferable.

The catalyst supported on the surface of the metallic honeycomb structure has a catalytically active substance supported on a carrier having a large surface area. Here, typical examples of carriers having a large surface area include γ-Al2O3-based, TiO2-based, SiO2-Al2O3-based, and perovskite-based carriers. Examples of catalytically active substances include noble metals such as Pt, Pd, and Rh, and Cu.
, Ni, Cr, Co, and other base metals. Among the above, 10% of noble metals are added to the γ-Al2O3 system.
It is preferable to carry up to 100 g/ft3.

The honeycomb shape of the honeycomb structure in the present invention is not particularly limited, but specifically, for example, 6 to 1500 cells/inch2 (cpi2) (0.
Preferably, the cell density is in the range of 9 to 233 cells/cm2. Also, the thickness of the partition wall is 50
A range of ~2000 μm is preferred.

Further, as mentioned above, the honeycomb structure may be porous or non-porous, and its porosity is not limited, but it should be in the range of 0 to 50%, preferably less than 25%, in order to improve its strength properties. , desirable in terms of oxidation resistance and corrosion resistance. Further, when supporting a catalyst, it is preferable to have a porosity of 5% or more from the viewpoint of adhesion with the catalyst layer. In the present invention, the honeycomb structure refers to an integral structure having a large number of through holes partitioned by partition walls, and the cross-sectional shape (cell shape) of the through holes may be any arbitrary shape such as circular, polygonal, corrugated, etc. shapes can be used.

[0025]

EXAMPLES The present invention will be explained in more detail below based on Examples, but the present invention is not limited to these Examples. (Example 1) Pure Fe powder, pure Cr powder, Fe-50wt
%Al alloy powder, Fe-20wt%B powder, Fe-75
wt%Si powder Fe-20Cr-5Al-1Si-0
．． The raw materials are blended to have a composition of 05B (wt%), an organic binder (methylcellulose), an antioxidant (oleic acid), and water are added to adjust the clay, and a honeycomb consisting of square cells is extruded. After drying, it was fired at 1350°C under H2 atmosphere, and the rib thickness was 4 mil and the number of through holes was 40.
A honeycomb structure of 0 cpi2 was obtained.

[0026] Outer diameter 90 mmφ obtained by the above method,
As shown in FIG. 7, electrodes 21 were set at two locations on the outer surface 20 of a honeycomb structure having a length of 40 mm. In addition, as shown in the figure, slits 22 with a length of 70 mm are provided at six locations in the axial direction of the through hole (the slit length at both ends is 5 mm).
0 mm), and the number of cells between the slits 22 is 7 (approximately 10
mm). Next, using a heat-resistant enamel slip S-6163S manufactured by Nippon Frit Co., Ltd., the outer surface 20 of the honeycomb structure and the outer peripheral portion 2 of the slit 22
Glaze was applied by dipping from 3 to 10 mm. S
-6163S is a slip made by adding 30% chromium oxide and 5% clay to a base frit mainly composed of SiO2 -BaO. The softening temperature of the base frit is 720℃,
The coefficient of linear thermal expansion is 8.2×10/-6°C. After glazing 1
Dry at 50°C for 16 hours, then dry at 1100°C in air for 5 hours.
A heat treatment was performed for a minute to obtain an enameled honeycomb heater 24 having a film thickness of 100 μm.

[0027] Slit outer peripheral part 2 of honeycomb heater 24
3 is further filled with an inorganic adhesive made of heat-resistant ZrO2, and the heater 24 is attached to the can body 30 as shown in FIG.
I set it up and got a heater unit. Furthermore, the surface 32 of the ring 31 that may come into contact with the heater 24 was also enameled in the same manner. (Enamel film thickness 100μm)
Further, a ceramic mat 33 (Interum (trademark) mat manufactured by Sumitomo 3M) was disposed between the can body 30 and the honeycomb heater 24.

(Example 2) Outer surface 20 of honeycomb structure
A honeycomb heater 24 was obtained in the same manner as in Example 1, except that the outer peripheral portion 23 of the slit 22 was not enamel-processed. On the other hand, S-6163 was enameled onto a T-shaped spacer 13 shown in FIG. 4 to be inserted 10 mm from the outer circumference 23 of the slit 22 of the honeycomb heater 24. This is the slit 22 of the honeycomb heater 24.
and set it in the can body 30 shown in FIG. 1 in the same manner as in Example 1 to obtain a heater unit. The spacer is made of ferritic heat-resistant stainless steel with a plate thickness of 0.8 mm (
100° C. thermal expansion 10×10 −6 /° C.) was used.

(Example 3) In the heater unit of Example 2, the inner portion 34 of the can body 30 was further enameled as shown in FIG.

(Comparative Example 1) A heater unit was obtained in the same manner as in Example 1, except that only a heat-resistant adhesive was filled in the outer circumferential portion 23 of the slit 22, and the ring 31 was not provided and the enamel was not enameled. .

(Comparative Example 2) Spacer 1 of slit 22
A heater unit was obtained in the same manner as in Example 2 except that a heater unit made of Al2O3 and having a thickness of 1.0 mm was used as Example 3, and the ring 31 was not provided and the enameling was not performed.

[Vibrating Burner Durability Test] The durability of the heater units and honeycomb kneaders of the above Examples and Comparative Examples was investigated by a vibrating burner durability test that simulated the durability of an actual vehicle. That is, using combustion exhaust gas from a propane burner (intake air amount 1 m3/min, propane 21 l/min), the heater temperature is raised from 100°C to 980°C in 5 minutes, and then lowered from 980°C to 100°C in 5 minutes. The cycle was repeated for 100 cycles. At this time, the heater unit was forced to 20G and 20G using a vibrator.
A vibration of 0 Hz was applied. The insulation status of the heater after the test is shown in the table below.

[0033]

As a result of the durability test of the vibrating burner, it was found that the heater unit and heater of the example maintained the resistance adjustment mechanism after the durability test, was able to maintain the insulation between the heater and the can body, and did not damage the heater mechanism. While it was possible to prevent deformation of the heater itself, all of the comparative examples lost their resistance adjustment function and could no longer be used as heaters.

[0035]

As explained above, according to the resistance-adjustable heater and heater unit of the present invention, short circuits can be prevented even under severe driving conditions of automobiles, and the insulation of resistance-adjustment mechanisms such as slits can be ensured. It has the advantage of being able to hold

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional explanatory diagram showing an example of a honeycomb heater of the present invention.

FIG. 2 is a partial explanatory diagram showing an example in which a ceramic coating is applied to the slits of a honeycomb heater.

FIG. 3 is a partial explanatory diagram showing an example in which a spacer is inserted into a slit of a honeycomb heater.

FIG. 4 is a partial explanatory diagram showing an example of a spacer.

FIG. 5 is a partial explanatory diagram showing another example of a spacer.

FIG. 6 is a partial explanatory diagram showing still another example of a spacer.

FIG. 7 is a perspective view showing an example of a honeycomb heater.

[Explanation of symbols]

10 slit portion, 11 outer peripheral portion, 12 coating, 13 spacer, 20 outer surface, 21
Electrode, 22 Slit, 23 Outer periphery, 24
Honeycomb heater, 30 can body, 31 ring,
32 faces, 33 mats, 34 inner parts.

Claims (14)

[Claims] 1. A resistance-adjustable heater comprising a honeycomb structure having a large number of through holes, at least two electrodes for supplying electricity, and a resistance adjustment mechanism between the electrodes, the resistance adjustment mechanism comprising: A resistance-adjustable heater characterized in that at least a portion of the heater is coated with an insulating ceramic coating. 2. The resistance-adjustable heater according to claim 1, wherein the honeycomb structure is made of metal. 3. The resistance-adjustable heater according to claim 1, wherein an insulating ceramic coating is applied to the outer peripheral surface of the resistance-adjustable heater. 4. The resistance adjustment type heater according to claim 1, wherein the resistance adjustment mechanism is a slit. 5. The resistance-adjustable heater according to claim 4, wherein a metallic spacer coated with an insulating ceramic is inserted into the outer periphery of the slit. 6. The resistance-adjustable heater according to claim 1, wherein the ceramic coating is applied by enameling. 7. A resistance-adjustable heater comprising at least two electrodes for supplying electricity to a honeycomb structure having a large number of through holes, and a slit serving as a resistance adjustment mechanism between the electrodes, wherein the slit A resistance-adjustable heater characterized by having a metallic spacer coated with an insulating ceramic inserted into the outer periphery of the heater. 8. A resistance-adjustable heater in which a honeycomb structure having a large number of through-holes is provided with at least two electrodes for supplying electricity, and a resistance-adjustable mechanism is provided between the electrodes is mounted in a metallic can body. The heater unit is characterized in that at least a portion forming the resistance adjustment mechanism, or at least a portion forming the resistance adjustment mechanism and the can body are coated with an insulating ceramic coating. heating unit. 9. The heater unit according to claim 8, wherein the honeycomb structure is made of metal. 10. The heater unit according to claim 8, wherein an insulating ceramic coating is applied to the outer peripheral surface of the resistance-adjustable heater. 11. The heater unit according to claim 8, 9 or 10, wherein the resistance adjustment mechanism is a slit. 12. The heater unit according to claim 11, wherein a metallic spacer coated with an insulating ceramic is inserted into the outer periphery of the slit. 13. The heater unit according to claim 8, wherein the ceramic coating is applied by enameling. 14. A resistance-adjustable heater comprising a honeycomb structure having a large number of through holes, at least two electrodes for supplying electricity, and a slit serving as a resistance adjustment mechanism between the electrodes, in a metal can. A heater unit held in a body, characterized in that a metallic spacer coated with an insulating ceramic is inserted into the outer periphery of the slit, and the can body is coated with an insulating ceramic coating. heating unit.